1. Field of the Invention
The present invention relates to a method for treating the surface of articles, such as silicon wafers, with a plasma jet. More particularly, the present invention relates to a method for moving a plasma jet tool relative to the surface of an article being treated by the plasma jet tool.
2. Description of the Prior Art
A plasma jet is a confined and very intensive heat source. Typically, plasma jet tools have a cross section or footprint which is significantly less than the cross sectional area of a surface of an article, such as a silicon wafer, being treated by the plasma jet. Prior art plasma jet treatment of articles typically involves the production of a plasma jet which is directed at the article's surface. While the plasma jet is directed at the article's surface, the plasma jet is moved relative to the surface, usually by linear scanning, such as an X-Y linear scan.
Such prior art plasma jet treatment methods using linear scanning can result in damage caused by local overheating of the surface. In the case of silicon wafers, local overheating can result in crystal structure defects, wafer melting, high temperature gradient induced stresses, and breakage. Also, with prior art plasma jet wafer treatment methods, providing uniformity of plasma jet treatment to wafers of differing dimension can be problematic.
More specifically, several deficiencies in prior art linear scanning methods include low throughput and high potential for wafer damage. Every linear movement of the plasma jet across the wafer produces hot lanes at the wafer surface with cold surfaces adjacent thereto. The hot lanes tend to produce high temperature gradients, which in turn causes stress in the wafer. In order to avoid high temperature gradients, a delay must be made between adjacent hot lanes to allow for partial cooling of a previous hot lane and lowering of temperature gradients to avoid wafer surface overheating or thermal stress induced wafer damage. As many linear scan movements have to be made to treat the entire wafer surface with sufficient delays to prevent thermal damage to the wafer, resulting wafer treatment throughput suffers.
The linear scan methods of the prior art also have the drawback that surface treatment quality suffers due to redeposition on the wafer surface caused by the contact of etch products with cold wafer surface near a hot lane.